Aye, Shanks has always been Roger's heir. Thats why hes the perfect one to test and challenge Luffy for Pirate King and the One Piece too. Both of them inheriting Roger's will, one of them more directly and the other indirectly. I'm sure Oda is saving Shanks for last for that too. Luffy vs Shanks on Laugh Tale for the One Piece would go SO HARD!